Lysosomal storage diseases are associated with significant morbidity and mortality in affected patients. Transplantation of normal bone marrow cells in these conditions may provide long-term enzyme replacement and lead to attenuation or reversal of organ system deterioration attributable to accumulated substrate. Preclinical studies of bone marrow transplantation (BMT) in storage diseases have hitherto been precluded by the lack of appropriate animal models. The twitcher mouse is a recently-described model of human globoid cell leukodystrophy (Krabbe disease; galactosylceramidase deficiency), a sphingolipidosis. Initial studies have shown that hematopoietic cell transplantation (HCT) from enzymatically normal congenic mice into 10-day-old twitcher mice is associated with prolonged survival and some remyelination in peripheral nerves. The proposed comprehensive studies will further examine the clinical, histopathological, neurochemical, and neurophysiological effects of HCT in twitcher mice. The survival and clinical course of groups of twitcher mice that receive HCT at various ages (2, 5, 7, or 10 days) will be compared with those of untreated twitchers. The activity of galactosylceramidase will be determined in brain, nerve, liver, kidney, spleen, spinal cord and plasma of untreated twitchers, normal littermates, and HCT-treated twitcher mice at selected times after HCT to determine the temporal course and extent of enzyme replacement. Levels of substrate (galactosylceramide and psychosine) will be analyzed in tissues and plasma after HCT. Histopathological and ultrastructural alterations in brain, spinal cord, and sciatic nerves in untreated and HCT-treated twitcher mice will be assessed by light and electron microscopy. The effects of HCT on the neurophysiologic status of twitcher mice will be studied by serial nerve-conduction measurements, using standard neurometric techniques, and compared with similar studies in untreated twitchers and normal littermates. The effects of injection of Sindbis virus, which erturbs the blood-brain barrier (BBB) by production of intense CNS inflammation, will be evaluated in untreated and HCT-treated twitcher mice; their clinical, biochemical, and neurometric status will be compared to those with mice that do not receive BBB disruption. The information thus obtained with HCT in a prototypic animal model of human sphingolipidosis is applicable to strategies for clinical enzyme replacement therapy, whether by cellular allotransplantation or gene insertion, in human lysosomal storage diseases.